There are numerous industrial operations which could be efficiently performed by a continuous press capable of applying pressure continuously to a workpiece while the workpiece is conveyed through the press. Of special interest is such a press suitable for sheet molding industrial resins or plastic compounds. Of particular importance is the ability to maintain a consistent high pressure to a molded part while it is being moved through the press and to apply heat as well.
A continuous press adapted for industrial processes is set forth in my U.S. Pat. No. 3,850,213. That patent discloses a continuous press comprising upper and lower platens which support opposed sets of presser-conveyor rails by means of plural cams which are rotatably mounted on the platen. Each set of rails drives a caterpillar belt and a sheet belt which encircle the platen supporting the set of rails. The workpiece is interposed between the sheet belts. The rails in each set are divided into plural groups and the supporting cams impart orbital motion to the rails in a poly-phase arrangement, i.e., the motion of each group of rails is phase displaced from the motion of each other group of rails. The corresponding groups of rails in the two opposed sets are actuated synchronously and the workpiece is pressed and advanced first by one group of rails in each set, then by another group of rails in each set. While this arrangement is capable of providing uniformly distributed, high pressure over the workpiece and a desired feed rate, it relies upon mechanical actuation through the sliding friction of rotating cams.
Another continuous hydraulic press is set forth in my U.S. Pat. No. 4,316,411. That patent discloses a continuous press similar to that of U.S. Pat. No. 3,850,213 in that it uses the groups of rails stepping in a poly-phase order, and a caterpillar belt and a sheet belt. The drive arrangement is hydraulic, each group of rail having separate but coordinated drive systems with linear actuators for applying pressure to the rails and for moving the rails transversely in the direction of belt movement and then relieving the pressure and moving the rails in reverse. The pressure applying actuators moved through a small angle during the belt movement so that the applied force was not always in a direction normal to the belts.
Another type of continuous press known in the art utilizes a pair of oppositely rotating chains of platens which are spaced apart to receive a workpiece therebetween. The platens are aligned in the direction of movement and are driven continuously over guide rollers or sprockets. Pressure is applied by hydraulic means to compress the workpiece between the opposed platens and an anti-friction roller belt is provided on the back side of each chain of platens to provide a roller type bearing. Such apparatus is disclosed in the U.S. Pat. Nos. 2,071,999 and also in the 2,490,819.
Another continuous press utilizes two oppositely disposed sets of parallel bars with the bar of each set extending in the direction of travel of the workpiece through the press. The workpiece is compressed between a pair of bars, one from each set, during a forward stroke of the pair of bars and then is compressed between a second pair of bars, one from each set, during a forward stroke of the second pair of bars. The bars of the first pair are caused to separate and relieve pressure on the workpiece and to make a return stroke during the forward stroke of the second pair. Similarly, the second pair of bars makes a return stroke during the forward stroke of the first pair. Apparatus of this type is set forth in the U.S. Pat. No. 2,340,607 wherein the bars are driven in the forward stroke by friction drive rollers and are released by the rollers at a flat spot thereon for a return stroke under the influence of a retracting spring, Another continuous press of this type is disclosed in the U.S. Pat. No. 2,289,022 wherein selected bars from the upper and lower set of bars are moved toward each other for compressing the workpiece therebetween by means of a cam and follower arrangement and the same bars are moved in a forward and return stroke on a common carriage which is actuated by a separate cam and follower arrangement.
Another apparatus using the reciprocation bar arrangement is shown in the U.S. Pat. No. 3,577,304. In the apparatus of this patent, a pair of opposed lifter bars are spaced apart to accept the workpiece therebetween and are mounted upon oppositely rotating eccentrics. Upon each rotation of the eccentrics the lifter bars successively compress the workpiece therebetween and impart a forward motion to it; at the end of the forward stroke the lifter bars open and a pair of holding bars are closed thereagainst by spring pressure to maintain compression of the workpiece in a dwell-condition while the lifter bars make a return stroke.
Another type of continuous press utilizes sliding friction to obtain a large bearing area for support of the moving press members. In this type of apparatus a pair of endless belts are disposed opposite each other and each is mounted on suitable drive rollers. The portions of the endless belts which are disposed in opposition and which receive the workpiece therebetween are respectively backed by rigid plates which in turn are supported by hydraulic plungers. To reduce the sliding friction the sheet of material having a low coefficient of friction is interposed between the moving belts and the respective backing plates. A continuous press of this type is shown in the U.S. Pat. No. 3,680,476.